This invention relates to machine tools in general and, in particular, to those of the class having a set of different, interchangeable cutting tools mounted at preassigned angular spacings on an indexing tool magazine for selective use. Still more particularly, the invention pertains to an automatic tool changing mechanism in such a class of machines whereby the cutting tools on the tool magazine are successively mounted to, and dismounted from, a spindle moving toward and away from work for performing various operations thereon.
While a variety of automatic tool changers have been suggested and incorporated with machine tools, each such device generally resolves itself into three basic components: (1) an indexing tool magazine holding a set of cutting tools; (2) a tool transfer mechanism for the transfer of each cutting tool between the tool magazine and the spindle; and (3) a chuck for holding each cutting tool on the spindle. These three tool changer components must operate in well timed relation to one another for efficient machining of the work with the successive cutting tools. Heretofore, the components have been fluid actuated and/or cammed, or have been driven by servomechanisms. All such conventional actuating mechanisms are unsatisfactory by reason of complexity in the construction and arrangement of the required parts.
Japanese Patent Laid Open (KOKAI) No. SHO-60-155338 describes and claims a more simplified tool changer. It teaches tool transfer between the tool magazine and the spindle by cam and crank mechanisms actuated by the travel of the spindlehead toward and away from the work. However, for the indexing of the tool magazine, this prior art tool changer employs a fluid actuator devoted exclusively to that purpose. The fluid actuator requires a valve, which may be solenoid operated, for incrementally revolving the tool magazine. Each time the tool magazine is incremented, the operation of the solenoid valve must be checked to make sure that the magazine has been driven a unit distance. Such fluid operated indexing of the tool magazine is not so reliable in operation and quick in response as the cam operated tool transfer between the tool magazine and the spindle.
Another inconvenience with the noted prior art tool changer manifests itself during the continuous indexing of the tool magazine. Each cutting tool is held by a pair of gripping jaws on the tool magazine and is released therefrom by a finger acting directly on the gripping jaws. The release finger is held close to the gripping jaws during the continuous indexing of the tool magazine. Consequently, in the event of the malfunctioning of the electrical control means, the release finger may strike a tool on the magazine, possibly dropping the tool therefrom or destroying the magazine.